Charles, if the windows are closed the drop in temperature during two or 3 minutes waiting for a light to change would not be noticable. And if it were ever found to be a problem a layer of urethane insulation sprayed on the inside of the body sheetmetal would drop heat loss by at least an order of magnitude, but it might add a dollar to the cost of building the car, so they could make it a $50 option. My point is that in a reasonably closed vehicle temperature change is not that fast. And of course there should be a means of inhibiting the automatic part of the stopstart system, since a computer is never able to handle unanticipated exceptions correctly.

Another good point, William K. If you live in the north, interior heating could also be a problem when the engine is shut down. Suppliers are talking about using an electric pump to circulate coolant to a heat exchanger in order to keep drivers and passengers from freezing during cold January nights.

Charles, that is why a constantly engaged system like the E-Assist woulld be such a logical choice. But if it could be done with a 12 volts only system instead of needing the higher voltage batteries then it could be much simpler. And store the excess regenerated power in a supercapacitor, since a regular battery is not able to accept charge at such a high rate.

And don't forget the challenge of running things with the engine off. That will be the limiting factor for stop-start operation.

I agree thta smart lights could save more energy. Here in NC, it seems that more than 50% of many of the light cycle time is spent with no movement through the intersection, while many cars are waiting.

First, this is indeed an interesting posting, and informative as well.

But stop-start can save a lotmore than the fuel burned waithing stopped for the light to change. Start stop can easily provide a 15% reduction in fuel consumption if coasting is added to the operation. Just consider how much more fuel can be saved if the engine switches off for coasting as well as when stopped. BUT that would require steering that did not get harder with the engine switched off, as well as brakes that did not need engine power for the boost. Solving those two problems would allow a real improvement.

Yes, start-stop makes a big difference, g-whiz. By itself, it's probably 5%; with regenerative braking, about 15%. In the din of all the electric car and hybrid news, start-stop often gets forgotten. Even so, it's still going to be big.

"Up to 15% fuel savings"? I always knew all those start/stops are killing fuel economy, thus the reason for different city/hwy mpg ratings. Why is there never any discussion on engineering our cities to reduce start/stops? All we seem to do is add traffic lights and traffic engineers are lazy and allow each traffic light operate independently as if they all were the only traffic light in town. Not all towns, but most. In my CA town, its takes 20 minutes to go 4 miles, due to the ridiculous number of start/stop/wait traffic lights.

Years ago, I had the pleasure of visiting Grants Pass, OR where all the traffic lights on the main drag are synchronized so that if you go the speed limit, you can drive all the way through town without ever stopping. Think of the fuel savings we could capture as a country if traffic engineers gave some thought on how to keep people moving through the system instead of adding start/stops.

Nice article Chuck, the CSIRO pioneered using lead acid batteries in conjunction with super capacitors to get around the problem, I wonder which path will win in the long term? Certainly the weight savings in Lithium will save some small amount of fuel as well.

I agree with you that start-stop makes some engineering sense, ockham, especially give the looming 54.5-mpg mandate. Even though 2025 sounds like a long way off, it's not that far away when you consider the development cycle of a vehicle, and the even longer development cycle of new technologies.

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